It is known from EP-A-1327776 an electronic starter device for an electric motor of a compressor of a household appliance, in the case in point a refrigerator or a freezer, in which a switch for supplying the starter winding is electronically controlled by a heat-sensitive element operatively connected to the switch; the heat-sensitive element is a thermistor or a PTC tablet and the switch comprises a TRIAC.
Such a starter device, in addition to being relatively complex and expensive, determines a relatively high energy consumption even after the motor has started, equal to approximately 1-1.5 watts, a consumption which is lower than the energy consumption of traditional starter devices based on heat-sensitive elements only, but still is not satisfactory.
EP 1045510B1 relates to an electronic starter device for an electric motor of a refrigerator compressor, in which a first and a second circuit branch, each of which is equipped with a resistor, a capacitor and a diode, are fed at AC to generate pulses having decreasing amplitude in time, which are used by means of amplifiers comprising two MOS transistors for driving the transistors themselves, such transistors both being operatively connected to switch means for supplying the electric motor starter winding, such a switch means being constituted by a TRIAC.
During the positive mains half-wave, the capacitor of the first branch is charged by means of the corresponding resistance and, by means of the diode, supplies to a first transistor the signal needed to bring the same to a conducting state, needed in turn by the latter to supply the TRIAC with the current needed to drive the motor starter winding. In the subsequent negative half-wave, the same process is activated in the second branch, supplying to a second transistor the signal needed to bring it to a conducting state and to continue to supply the necessary current to the TRIAC. When the two capacitors have reached the maximum charge voltage, the flow of current terminates and the TRIAC, by switching off, shuts down the feeding of the compressor motor starter winding. Resistors arranged in parallel on the capacitors of the two branches ensure that at the next start-up, the two capacitors are discharged and ready to be charged again.
Neither is the above-described solution of EP 1045510B1 entirely satisfactory. Indeed, although on one hand such solution allows to obtain nearly zero energy consumption when the motor starter winding is not fed, on the other hand, the resulting electronic circuit is relatively complex and expensive to make, requires components not commonly used in consumable electronic circuits, needs a relatively cumbersome electronic board for its implementation and may be difficult to calibrate.